School Science Lessons
Topic 18a
2018-11-02
Please send comments to: J.Elfick@uq.edu.au18a Swimming pool chemistry18.1.0 Chemicals used in swimming pools18.2.0 Chlorine used in swimming pools18.3.0 pH of swimming pools18.4.0 Management of swimming pools18.5.0 Tests for swimming pools18.1.0 Chemicals used in
swimming pools
See: Chemicals (Commercial)18.7.15 Algicides, control of algae in swimming
pools18.7.38 Biguanides sanitizers18.7.19 Bromine products, HBrO18.7.2.2.1 Calcium hypochlorite, Ca(OCl)218.7.23 Chloramines in swimming pools18.7.14 Cyanuric acid, conditioner, stabilizer18.7.2.4 Dichlor18.7.2.2 Inorganic hypochlorites18.7.42 Stains in swimming pools18.7.45 Lithium hypochlorite18.7.50 ORP (Oxidation-Reduction Potential)18.7.11 Oxidizing agents18.7.51 Oxidizers18.7.53 Phenol red18.7.56 QAC (quaternary ammonium compounds:)18.7.37 Redox potential18.7.52 Ozonator18.7.57 Sequestering agent, chelating agent18.7.58 Sodium bicarbonate18.7.2.2.2 Sodium hypochlorite,
NaOCl18.7.59 Sodium carbonate18.7.60 Sodium dichlor18.7.61 Sodium monopersulfate18.7.62 Sodium persulfate18.7.63 Sodium sulfite18.7.64 Sodium thiosulfate18.7.67 Trichlor18.7.69 Zeolite18.2.0 Chlorine used in swimming pools
See: Water Testing (Commercial)18.7.2.0 Chlorination of swimming pools12.19.8 Chlorine experiments18.7.5 Available chlorine18.7.1.0 Chlorine and water18.7.28 Chlorine demand18.7.29 Chlorine enhancer18.7.2.1 Chlorine gas in swimming pools18.7.30 Chlorine generator18.7.12 Chlorine levels in swimming pools18.7.31 Chlorine lock18.7.13 Chlorine lost by ultraviolet radiation18.7.32 Chlorine neutralizer18.7.2.3 Chlorinated isocyanurates18.7.2.5 Chlorinating concentrates18.2.7.6 Chlorinating tablets, chlorinating concentrate18.7.26 Chlorinator18.7.25 Combined chlorine18.7.17 Cost of chlorinating18.7.6 Dissolve chlorine in swimming pool water
by electrolysis18.7.15.1 Green hair and faded hair from swimming
pools 18.7.21.3 Methyl orange test for chlorine in
swimming pools18.7.27 Stabilized chlorine18.7.8 Superchlorination, shock treatment, breakpoint
chlorination18.7.21.0 Test kit for chlorine levels in swimming
pools18.7.4.0 Tests for free chlorine in water18.7.24 Total chlorine in swimming pools18.3.0 pH of swimming pools
See: pH (Commercial) 18.7.21.1 Acid demand of swimming pools 18.7.9 Alkalinity, total alkalinity and buffer
capacity18.7.10 Adjusting the pH of swimming pool water18.7.3 Hypochlorous acid, HOCl18.7.7 Swimming pool water and pH18.4.0 Management of swimming
pools3.9.2 Checklist of daily routine for
the swimming pool operator18.7.21.1 Acid demand of swimming pools18.7.39 Contaminants in swimming pools18.7.40 Corrosion in swimming pools18.7.41 Defoamers18.7.33 Disinfectants9.242.0 Expired air resuscitation,
(EAR)18.7.47 Fill water, makeup water18.7.20 Filters18.7.34 Ionizers for swimming pools18.7.43 Langelier saturation index18.7.44 Liquid acid for swimming pools18.7.46 Magnesium hardness18.7.47 Make-up water18.7.48 Marbelite18.7.35 Nitrogen pollution18.7.49 Non-chlorine shock, potassium peroxymonosulfate18.7.36 Organic waste9.242.0 Resuscitation18.7.18 Stabilized and unstabilized swimming pools18.7.22 Starting to use a filled swimming pool18.5.0 Tests for swimming
pools18.7.9 Alkalinity, total alkalinity and buffer capacity18.7.21.6 DPD test for swimming pools, diethyl-paraphenylene
diamine18.7.21.3 Methyl orange test for chlorine in
swimming pools18.7.21.5 OTO test for swimming pools, orthotolidine18.7.21.0 Test kit for chlorine levels in swimming
pools18.7.16 Total dissolved solids (TDS) water hardness,
scale18.7.65 Suspended solids18.7.66 Total dissolved solids18.7.68 Turbidity18.7.70 Water hardness18.7.0 Swimming pool chemistry
A swimming pool system lacks the three purifiers that protect water quality
in natural bodies of water:
1. Aeration, the addition of oxygen to the water from the continuous flow
of water through lakes, streams and rivers.
2. Dilution of sediment from continuous water flow.
3. Prevention of contaminant build-up by water flow, movement and dilution,
and biodegradation by aquatic organisms.
As a swimming pool lacks these purifiers, it is subject to rapid stagnation.
Also, it is usually contaminated with bacteria, algae, dust and dirt,
and organic materials from swimmers wastes, sweat, urine and faeces.
A swimming pool must be disinfected as part of a total system to remove
bacteria, algae and organic contaminants leaving water with
acceptable clarity and colour.
Volume of a swimming pool length × width × depth.
If length 25 m, width 10 m, depth 1 m to 2 m (average 1.5 m),
then volume = 25 × 10 × 1.5 = 375 cubic metres (375 000 litres).18.7.1.0 Chlorine and water
When chlorine is added to water, a mixture of hypochlorous acid, HOCl,
the active sanitizing species, and hydrochloric acid, HCl,
forms within seconds at room temperature.
Cl2 (aq) + 2H2O <=> HOCl + Cl-
+ H3O+
chlorine + water <=> hypochlorous acid + chloride ion + hydronium
ion
In dilute solution and pH > 4, the equilibrium displaces to the right,
and little Cl2 exists in solution.
The chlorine added to swimming pool water does not produce a concentrated
solution of a strength to yield such a low pH.
However, the oxidizing property of the added chlorine is in the HOCl formed
and produces the main disinfecting action of added
chlorine solutions.
Hypochlorous acid dissociates almost instantaneously into hydrogen and
hypochlorite ions.
The reaction is reversible.
The dissociation depends on the pH and temperature.
Hypochlorous acid exists in a pH dependent equilibrium with hypochlorite
ion (OCl-) in swimming pool water.
H2O + HOCl <=> H3O+ + OCl-
water + hypochlorous acid <=.> hydronium ion + hypochlorite ion.18.7.2.0 Chlorination of
swimming poolsSee diagram 13.4.2: Distribution of HOCl and
OCR- in water at pH levels
Most swimming pools are sanitized with chlorine-based compounds.
When chlorine compounds are dissolved in water, hypochlorous acid forms,
which does the actual sanitizing.
In most cases, the non-chlorine part of the chlorine compound serves no
other purpose than to hold the chlorine until the product
dissolves.
The three categories of sanitizer contain chlorine in different forms.
All three sanitizers are compatible and effective with other chemicals
in swimming pool water.
Each will do its function without causing objectionable tastes, odours
or colours in the water, if properly applied.
Swimming pool chlorine may be calcium hypochlorite or sodium hypochlorite.18.7.2.1 Chlorine gas in
swimming pools
Chlorine is a member of the halogen family of sanitizers.
Its use in swimming pools is in the form of a gas, as a liquid, in granular
or tablet forms.
When added to swimming pool water it acts as an oxidizer, sanitizer,
disinfectant and biocidal agent.
Chlorine gas is referred to as having 100% available chlorine, is relatively
low cost and is used in public swimming pools and most
bulk drinking and waste water treatment systems.
However, it is a gas that must be delivered in bulky metal cylinders and
has to be applied to the water through sophisticated metering
systems operated by trained personnel.
It is highly corrosive, toxic, and very acidic because of the H3O+
and Cl-.
Operators of regulated public swimming pools may be required to install
separate feeding equipment to add soda ash to neutralize the
acidity from the chlorine gas.
If chlorine gas were the only chemical available to disinfect water,
there would be few home swimming pools.18.7.2.2 Inorganic hypochlorites
Hypochlorites including calcium hypochlorite, sodium hypochlorite and
lithium hypochlorite are used as a disinfectant, sanitizer,
bactericide, algicide and oxidizer in swimming pool water.
Calcium hypochlorite is also used as a disinfectant in drinking water.18.7.2.2.1 Calcium hypochlorite,
Ca(OCl)2
Calcium hypochlorite, in bleaching powder (30% chlorine), chlorinated lime
(OXD 2208)
Calcium hypochlorite, Ca(OCl)2, 65% available chlorine, white
granular powder or compressed into pucks, pH 11.8, also contains
5 to 8% of insoluble material, which can cause cloudy water.
A by-product of this reaction is the calcium ion (Ca2+), a
major component of water hardness, and a contributor to scaling
tendencies in the swimming pool.
Ca(OCl)2 + H2O, Ca2+ + 2OCl-
+ H2O
calcium hypochlorite + water + calcium ion + hypochlorite ion + water.18.7.2.3 Chlorinated isocyanurates
Chlorinated isocyanurates, stabilized chlorine, are a group of chlorine
swimming pool sanitizers that contain stabilizer (cyanuric acid or
isocyanuric acid) as the granular form dichlor 56% available chlorine
and the tablet or stick form trichlor 90% available chlorine, the
latter usually used in a chlorine feeder.
Chemical feeder: a device that dispenses chemicals into the swimming pool
water at a predetermined rate.
Some provide chlorine or bromine, while others add cyanuric acid (CNOH)3,
also called conditioner and stabilizer.
A granular chemical added to the swimming pool water, which provides a
shield to chlorine for protection from the UV radiation from
the sun.
It is also found in dichlor / trichlor products.18.7.2.4 DichlorSee diagram 16.13.8: Trichloroisocyanuric
acid, TCCA, C3Cl3N3O3, white
crystalline powder, disinfectant, bleaching agent
"Dichlor" is the common name for dichloroisocyanuric acid, C3HCl2N3O3,
or the active ingredient in dichlor cleansing powder sodium
dichloroisocyanurate C3Cl2N3NaO3.
Dichlor is a quick dissolving chlorine compound made up of chlorine and
cyanuric acid (stabilizer) and has a pH of 6.9.
Shock treatment with dichlor is not recommended as it may result in over
stabilization and chlorine lock.
If dichlor is used, a monthly check of the cyanuric acid level is recommended,
to prevent over stabilization and chlorine lock.18.7.2.5 Chlorinating concentrates
Both the granular and tablets forms are based on cyanuric acid (CNOH)3,
composed of alternating C and N atoms.
In the granular form two atoms of chlorine are added, giving an available
chlorine of 56%.
It is a sodium salt, so it has excellent solubility at 26.1% w / v and
a nearly neutral pH of 6.7.
It may be added directly to the swimming pool by hand broadcasting or it
can be pre-dissolved and added as a hypochlorite solution.
The tablet form contains three atoms of chlorine, giving it 90% available
Cl2.
It has a relatively low pH of 2-3 and high available chlorine content,
so much less needs to be added.
It has a minimal impact on pH and its low solubility of 1.2% w / v makes
it ideal for use in tablet form in continuous feeding systems.
The trichloro product should not be added directly to the swimming pool
in either its tablet or granular form,
because its high available chlorine, slow solubility and acidic pH give
it the potential to bleach, or pit any swimming pool surfaces
Both products are free of insoluble residues, produce a minimal impact
on pH and do not contribute to water hardness or scaling.
After the chlorine has been consumed in performing the sanitizing functions,
the cyanuric acid remains dissolved in the water to provide
maximum stabilization for the free chlorine residual.
Secondary chemical treatment with substances that control pH and buffer
the swimming pool, is also needed for swimmer comfort.
Depending on swimming pool conditions, secondary treatment might include
decolourizing, additional algicide, and chemicals to adjust
mineral levels (hardness) or retard evaporation.18.2.7.6 Chlorinating tablets,
chlorinating concentrate
Pool chlorinating concentrates provide the effectiveness of HOCl, the
ease and convenience of concentrated solids, and the benefits of
stabilization, to provide outstanding water quality with minimum effort
and expense.
Granular compounds react with water to produce the same active sanitizing
species, hypochlorous acid.
Therefore, it is an effective bactericide and algicide that will oxidize
organic contaminants.
Tablets react similarly, but produce three units of hypochlorous acid.
Both the granular compounds and tablets have a by-product, cyanuric acid,
which is supposed to stabilize free chlorine residual
without interfering with its sanitizing effectiveness.
However, the binding action of cyanuric acid reduces the concentration
of free available chlorine and demonstrably reduces sanitizer
efficiency.
Pool owners who use cyanuric acid must have higher free residual chlorine
to compensate for this fact so that sanitizer efficiency is
maintained.
Some Australian States have banned the use of cyanuric acids.
So to describe cyanuric acid products as a "conditioner" is misleading.18.7.3 Hypochlorous acid,
HOCl
Hypochlorous acid, HClO, is the active form of chlorine in swimming pool
water.
Hypochlorous acid is a weak acid and dissociates poorly below pH 6, so
it exists mainly as HOCl at low pH.
Between pH 6.0 and 8.5, a very sharp change occurs from undissociated
HOCl to almost complete dissociation.
At 20oC and pH greater than 7.5, hypochlorite ions, OCl-,
predominate.
HOCl is about 100 times more effective as a sanitizer than OCl-
because the negative charge on the OCl- ion hinders it entering
living
cellular structures and oxidizing the contents.18.7.4.0 Tests for free
chlorine in water
Free chlorine (free available chlorine, free residual chlorine, residual
chlorine) is the amount of chlorine left in the swimming pool water
after the chlorine demand has been satisfied.
It is the amount of free chlorine in the swimming pool water that is available
to oxidize, sanitize or disinfect the water.
Free chlorine is active chlorine and is not combined with any other molecule,
e.g. ammonia.
It is free to kill bacteria and algae in a swimming pool and is the chlorine
available to do its job of sanitizing the water.
A portion of the free available chlorine is present as hypochlorous acid,
which reacts to destroy organic material in the swimming pool
water.
The standard method for determining free chlorine is to measure the amount
of oxidant by its ability to liberate iodine from acidified
iodide solution.
Titrate a water sample with a standard iodide solution and detect the
iodine released by the blue colour formed with a fresh starch
indicator.
Find the amount of iodine released by back titration with sodium thiosulfate,
hypo.
The reagent is only oxidized to tetrathionate by the iodine.
With chlorine it is oxidized to sulfate.
HOCl + 2I- + H3O+ --> Cl-
+ I2 + 2H2O
hypochlorous acid + iodide ion + hydronium ion --> chloride ion + iodine
+ water
I2 + 2S2O32- --> S4O62
-+ 2I-iodine + thiosulfate ion --> tetrathionate ion + iodide ionDevices called rapid test meters can be used to test for chlorine
and pH.
With a DPD test kit, DPD1 shows free available chlorine and DPD3 shows
total chlorine.
The difference, if any, is the level of combined chlorine.18.7.5 Available chlorine
Available chlorine content is the term used to compare the amount of oxidizing
power that products containing chlorine have
compared to gas chlorine (Cl2).
It permits easy comparison of relative values of chlorine compounds.
Available chlorine is the amount of free chlorine that is available to
sanitize or disinfect the water.
It is also called Residual Chlorine and Free Available Chlorine.
When chlorine gas dissolves in water, it forms hydrochloric acid and hypochlorous
acid.
Since only the hypochlorous acid sanitizes, only half the chlorine added
to the water is usable.
Chlorine gas is defined as 100% available chlorine, so compounds for which
all the chlorine in solution is active will have percentages
twice the value based on composition.
Ca(OCl)2, which is 99.2% available chlorine for the pure material
may be quoted as 100% available chlorine.
It produces two moles of active chlorine compared to only one mole from
Cl2.
However, it has more than twice the molecular mass, a ratio of 143: 71.
So, on a mass basis, both chlorine gas and calcium
hypochlorite are equally effective.
Materials releasing other oxidizing agents when dissolved in water have
available chlorine defined in the same manner.
Approximate percentage available chlorine of substances added to swimming
pool water are as follows:
Cl2 chlorine gas 100% (by definition)
Bleaching powder (chloride of lime) 35%
Ca(OCl)2 calcium hypochlorite 99%, industrial products 70%
NaOCl, sodium hypochlorite 95% (solution 100%)
Bleach (industrial product) 12%
Bleach (household product) 3%
ClO2, chlorine dioxide 263%
NH2Cl, monochloramine 138%
NHCl2, dichloramine 165%
CONClCONClCONCl, C3Cl3N3O3,
trichloroisocyanuric acid 91%
CONClCONClCONH, dichloroisocyanuric acid 72%
CONClCONClCON- Na+, sodium dichloroisocyanurate
64%.18.7.6 Dissolve chlorine in
swimming pool water by electrolysis
See: Salinity, (Commercial)
Add common salt to water at concentration of approximately 4000 ppm to
generate hypochlorous acid continuously with an
electrolysis cell.
The water will gradually become basic so you must add an acid to keep
the pH between 7.2 and 7.8 for optimum swimmer comfort
and to maintain sanitizer efficiency.
Cathode (-) reaction: 2e- + 2H2O --> 2OH-
+ H2 (g)
water --> hydroxyl ion + hydrogen gas
Anode (+) reaction: 2Cl- --> Cl2 (g) + 2e-
chloride ion --> chlorine gas
Overall Reaction: 2Cl- + 2H2O --> Cl2
(g) + H2 (g) + 2OH-
chloride ion + water --> chlorine gas + hydrogen gas + hydroxyl ion.18.7.7 Swimming pool water
and pH
See: pH (Commercial)
Lower the pH of the swimming pool below pH 7 to increase the oxidizing
strength of the HOCl but more acidic solutions will corrode
many components .
For tiled swimming pools, the recommended pH range is pH 7.4-8.0 and you
must add about 200 mg / L calcium chloride to offset
removal of calcium salts from the grouting between the tiles.
A test for chlorine in water may measure the free residual chlorine or
the free residual chlorine plus the chloramines, which are termed
combined chlorine.
The lower the pH, the more readily chloramines form.
Above pH 7 few chloramines form, so keep the pH above 7.18.7.8 Superchlorination,
shock treatment, breakpoint chlorinationSee diagram 13.4.2: Chlorine dosage and residual
chlorine for breakpoint chlorination
Superchlorination is adding 7 to 10 times the normal dose of chlorine
to the swimming pool water to destroy ammonia, nitrogen,
chloramines and other contaminants.
Shock treatment is adding large amounts of an oxidizer such as chlorine,
hydrogen peroxide or potassium peroxymonosulfate to the
swimming pool water to destroy ammonia and nitrogen compounds, chloramines
and other contaminants.
Superchlorination is used to get rid of chloramines.
When HOCl is added to pool water at first chloramines form by reaction
with nitrogen compounds from humans.
With increased concentration of HOCl the chloramines are destroyed as
in the following equation with the products being off-gassed.
However, with excess HOCl, the chlorine concentration in the water rises
as chlorine no longer combines with organic compounds.
2NH3 + 3HOCl --> N2 (g) + 3HCl + 3H2O
ammonia gas + hypochlorous acid --> nitrogen gas+ hydrochloric acid
+ water
When chlorine in its various forms is added to water, it is used up in
oxidizing any material for which it is a sufficiently strong oxidizing
agent, e.g. iron II, sulfide, nitrite.
Next, chloramines, called combined chlorine, form from reactions of chlorine
with organic nitrogen compounds.
The breakpoint when further addition of chlorine is not used to oxidize
nitrogenous compounds, but remains as free available chlorine.
When you superchlorinate or shock treat your swimming pool, the goal is
to reach a high enough level of free chlorine to break apart
All molecular bonds, specifically the combined chlorine molecules, ammonia
or nitrogen compounds and to completely oxidize all
organic matter.
If you add enough chlorine to achieve this breakpoint chlorination, chlorine
added after that point will be free available chlorine.
Superchlorination refers to further additions of chlorine that will remain
in the water as residual chlorine to react with any material later
added to the swimming pool water.
Maintain a free chlorine residual at all times to achieve sparkling clear,
sanitary swimming pool water by periodic super chlorination of
the swimming pool water.
When chloramines are removed, better efficiency of chlorine is achieved.
More of the chlorine residual can then exist as the free or active form,
rather than as the less effective combined form.
You can use potassium monopersulfate for strong oxidation reactions to
oxidize any chloride ion back to chlorine.
Superchlorination is the remedial action that should be taken when the
DPD test detects the presence of 0.2 ppm or greater of
combined chlorine in the swimming pool.
Superchlorination simply involves the addition of 5 to 10 × normal daily
dose of chlorine.
Super chlorination should be routinely performed on very hot days under
heavy loads after heavy rains or if DPD test shows combined
chlorine in excess of 0.2 ppm combined chlorine.
Superchlorination is a remedial action and is recommended to remove gross
amounts of chloramines, correct eye and nasal
discomfort, or destroy a visible algae growth.
It also eliminates waiting, vacuuming, scrubbing and back washing to remove
algae appeared while chloramines accumulated.
However, although it works well, eventually if you keep loading chemicals
and contaminants in a swimming pool you problems.18.7.9 Alkalinity, total alkalinity
and buffer capacity
See: Buffer Solutions (Commercial)See diagram 13.4.2: Titration of sodium carbonate
with hydrochloric acid12.3.0.5 Ionization reaction of carbonic
acid
Alkalinity is the total amount of dissolved alkaline compounds in swimming
pool water.
Alkalinity is used a measure of the buffer capacity of swimming pool water,
i.e. the resistance to change in the pH of water when
strong acids or bases are added.
If the alkalinity is too low, pH control is difficult, because the pH
is sensitive to small amounts of acid and base.
Calculate how much 0.1 M hydrochloric acid would be needed to change the
pH by one unit if there is no buffering capacity.
The pH 8.4 of sodium bicarbonate in water lies between the pK values of
the first and second dissociation constants of carbonic acid,
3.60 and 10.25.
Carbon dioxide constitutes about 0.033% of the atmosphere and dissolves
in rainwater to form carbonic acid and produce theoretical
pH value pH 5.65.
Carbonic acid has two acidic hydrogens and hence has two dissociation
constants, PKa1 and PKa2.
H2O (l) --> H+ (aq) + OH- (aq)
2H+ (aq) + CO32- (aq) --> H2CO3
(aq) carbonic acid
CO2 + H2O --> H3O+ + HCO3-
HCO3- + H2O --> H3O+
+ CO32-
CO2 + H2O --> H2CO3 carbonic
acid
H2CO3 --> HCO3- + H+
Ka1 2.5 × 10-4 mol / L, Pka1 3.60
HCO3- --> CO32- + H+
Ka2 5.61 × 10-11 mol / L, PKa2 10.25
Total equation: CO2 + H2O --> HCO3-
+ H+Total equation KA = 4.30 × 10-7, PKa = 6.36, but call
this value the acidity constant.
Total alkalinity is a measure of the buffering capacity of swimming pool
water, i.e. resistance to change in pH of the water when acid
is added.
It is usually expressed as carbonate alkalinity, the total amount of alkaline
materials present in the water, principally hydroxides,
carbonates and bicarbonates.
Control of pH can be simplified by maintaining total alkalinity in the
range of 80 to 150 ppm.
Total alkalinity is composed of carbonates, bicarbonates, and hydroxides,
and functions as a buffer to help keep pH in the proper range.
Total alkalinity is easily measured with a test kit, and can be adjusted
with alkalinity control or acid according to label directions.
When you measure the total alkalinity, only measure the carbonate alkalinity
level.
The term "alkalinity" comes from the common use of sodium bicarbonate
as a buffer and its alkaline pH of 8.4.
However, you can also use acid buffers and so "buffer capacity" may be
a better term than "alkalinity".
If the swimming pool has an unstable pH, the total alkalinity should be
tested and adjusted.
The ideal total alkalinity range for swimming pools containing either
calcium or sodium hypochlorite is between 60 and 120 mg / L with
the optimum between 80 and 100 mg / L.
Total alkalinity too low
A swimming pool with low alkalinity, below 60 mg / L, will require the
addition of a little acid to cause a rapid reduction in pH.
A constant pH in low alkalinity water is difficult to maintain after rain.
Low buffering capacity causes corrosion and pH bounce, i.e. the pH resumes
previous levels soon after adjustment because the
buffering capacity is too low.
Raise total alkalinity by addition of an alkalinity control base, e.g.
sodium bicarbonate, that in turn increases the buffering capacity of
the swimming pool.
To raise alkalinity with sodium bicarbonate, the dosage calculation is
based on tables prepared for the swimming pool industry.
For example, a 25 000 L swimming pool would need 445 g of 57% sodium bicarbonate
to increase alkalinity by 10 mg / L.
You can add 80 to 120 mg / kg of the white powder sodium bicarbonate as
a buffering agent to raise the total alkalinity of swimming
pool water without having much affect on pH.
It will only increase pH up to 8.4, regardless of the quantity used.
Avoid adding large quantities at one time.
Total alkalinity too high,
A swimming pool with high alkalinity, over 120 mg / L, requires the addition
of large quantities of acid to produce a drop in pH.
It will tend to retain pH in most conditions and cause staining, scale
deposits and difficulty in adjusting pH.
High buffer capacity requires large amounts of acid or base to change
the pH of the solution.
If the pH rises rapidly even after the addition of large amounts of acid,
the buffering capacity is too high.
Reduce total alkalinity to 80 ppm by addition of granular addition of
PH minus or hydrochloric acid (muriatic acid) or sodium bisulfate
(sodium bisulfate, sodium hydrogen sulfate) granular dry acid, a dry white
crystal that is safer to handle than hydrochloric acid.
To lower alkalinity with hydrochloric acid or sodium bisulfate, the dosage
calculation uses tables to find the volume of hydrochloric
acid required to lower alkalinity.
The weight of sodium bisulfate, dry acid, required is found by multiplying
the volume of hydrochloric acid by 1.2.18.7.10 Adjusting the pH
of swimming pool water
The ideal range for pH in swimming pools is 7.0 to 7.6.
The pH of human tears is 7.2 to 7.4.
Measure the pH with an indicator that changes colour at a suitable pH.
The indicator is a weak acid that shifts from one colour to the other just
as hypochlorous acid shifts from HOCl to OCl-.
Use an indicator with the same pKa as hypochlorous acid.
The pH of natural water is about pH 5.6 because dissolved carbon dioxide
from the air forms carbonic acid that lowers the pH.
The continuous addition of hypochlorite powder will raise the pH, so you
must add "swimming pool acid" after some time,
e.g. the solid "swimming pool acid" sodium hydrogen sulfate, NaHSO4.
You can add hydrochloric acid to salt water swimming pools with electrolyzers.
A neutralizer is a chemical used to deactivate or destroy chlorine or bromine
used in better test kits to increase the accuracy of the
swimming pool water tests.
Base demand is a titration test used to find the amount of a base (alkali)
required to increase the pH to the correct level.
Base demand determined by a titration to find the amount of a base (alkali)
required to increase the pH to the correct level.
Sodium bicarbonate is used as a base to raise the pH, but sodium carbonate
is more effective and more commonly used.
The adding of sodium bicarbonate to water gives pH 8.4, but adding sodium
carbonate to water gives pH 11.6.
The addition of acid changes the pH according to the titration curve diagram.
The pH of swimming pool water may be changed from pH 7.2 to 7.8 by rain,
dust, swimmer wastes and addition of sanitizer.
However, a stabilized granular form of sanitizer, with a pH of between
6 and 7, will have little effect on the pH of swimming pools.
Stabilized swimming pool chlorine tablets, although low in pH, have a minimal
effect on pH because their high available chlorine and
stabilization means far less is needed to provide effective sanitation.
Chlorine gas, calcium hypochlorite, and liquid bleach all require greater
pH adjustment because their pH is far from the desired
operating range of pH range 7.2 to 7.8.
This pH range must be maintained because of its impact on sanitizer efficiency,
swimmer comfort, corrosion and scaling.
Since total alkalinity affects the amount of pH adjusting chemical added,
it should first be adjusted to the 80-125 ppm range.
After adjusting swimming pool chemistry, pH balance should be checked with
pH adjusting chemicals to protect chlorine from UV rays.18.7.11 Oxidizing agentsSee: Standard
electrode potential, electrode potential, reduction potential, E0See diagram 13.4.2: Reduction potential of
chlorine in water and pH
The ability of a material to oxidize is measured by the standard half
cell reduction potential, in volts.
This is an equilibrium value given for very specific conditions and so
gives only a general indication for a practical situation.
The larger the half cell reduction potential, the stronger the oxidizing
agent.
The standard electrode potentials, E0 are reference to a standard
electrode, usually the hydrogen electrode, which is arbitrary defined
as 0 V.
The oxidizing agent HOCl is stronger than OCl-.
HOCL + H3O+ + 2e- < = > Cl-
+ 2H2O, E0 = 1.49 V
ClO- + 2H2O + 2e- < = > Cl-
+ 2OH-, E0 = 0.94 V
It is dangerous to store hypochlorite powder swimming pool chlorine near
materials that can burn because it is a strong oxidizing agent.
If the material comes in contact with something that can be oxidized with
chlorine, e.g. brake fluid, then a fire can occur.
Chlorine gas is released when solid hypochlorite powder comes in contact
with moisture at any pH.18.7.12 Chlorine levels in
swimming pools
Free chlorine must remain in the swimming pool after all the organic material
has been oxidized, so measuring free chlorine is necessary.
This is usually done with test kits, e.g. using OTO, ortho-tolidine
(4, 4'-diamino-3, 3'-dimethylbiphenyl) or DPD
(Diethyl-paraphenylene diamine).
A chemical reagent used to test the total chlorine level in water at normal
temperatures.
It can measure free available chlorine if the water is first cooled to
1oC.
Its results depend on pH, time and concentration of chlorine.
Because of its toxicity, the use of OTO is restricted or prohibited in
many western countries.
It is chemically similar to benzidine without the methyl groups, a bladder
carcinogen.
The colour test with chlorine works well with laboratory solutions of
chlorine in water.
The reagent also reacts slowly with chloramines, the compounds that chlorine
forms when reacting with nitrogenous body waste
products in swimming pools.
So the free chlorine must be measured above what has reacted with waste
otherwise under dosing of chlorine may cause ear, eye and
throat infections increases because insufficient free chlorine exists
in solution.
Breakpoint chlorination occurs when free chlorine and combined chlorine
are simultaneously minimized.
Addition of further chlorine gives free chlorine.
Beyond which point nitrogenous compounds have been oxidized, principally
to nitrogen gas.
The methyl orange test measures free residual chlorine (HOCl + OCl-)
but the OTO test kit measures the combined chlorine,
as well, but you must do the test quickly.
Add chlorine solution to ammonia to form chloramines.
Make a stock solution of 0.2 g of Ca(OCl)2 per litre (1.78
× 10-3 M) as stock solution.
Dilute by a factor of five for use (3.5 × 10-6 M or 25 mg /
kg Cl2 equivalent).
Add the stock solution in 20 mL aliquots to 1 mL of 0.015 M NH3
solution (255 mg / kg).
A concentrated ammonia solution keeps the volumes almost constant.
Test with indicators.
Methyl orange will not bleach until about 2 mole equivalents of chlorine
have been added (about 80 mL), and free HOCL is present.
OTO, on the other hand, will show off scale from the beginning, indicating
reaction with chloramines as well.
Note the time taken by the oxidation reactions.
Measure a chlorine solution as a control to monitor any loss of chlorine.
Chlorine meters do not measure HOCl concentration.
They measure ORP and via an algorithm approximate HOCL concentration.
The reading may be unreliable.18.7.13 Chlorine lost by
ultraviolet radiationSee diagram 13.4.2: Ultraviolet absorption
spectrum of swimming pool chlorine
Reports suggest that in strong sunlight, up to half of the HOCl is destroyed
within 17 min.
Chlorinated sanitizer will produce HOCl, but up to 97% of that residual
can be lost in 2 hours so when 4-5 ppm of free available
chlorine is added as calcium hypochlorite at 6 am, it will be completely
gone by 12 noon, whether or not anyone uses the swimming
pool.
This same wasteful chlorine consumption occurs with chlorine gas and sodium
hypochlorite.
The free available chlorine residual could be maintained by testing the
water at noon, adding another 4-5 ppm residual for safe
afternoon swimming, then repeat the process at 6 pm to use the swimming
pool in the evening or install a chemical feeding system to
constantly add sanitizer.
Photolysis reaction
2OCl- + νuv --> 2Cl- + O2
(g)
2HOCl- + νuv --> 2HCl + O2 (g).18.7.14 Cyanuric acid, conditioner,
stabilizer
| See diagram 18.7.14: Cyanuric acid (CNOH)3
| See diagram 18.7.14a: Dichlorocyanuric
acid, "dichlor"
(Also: isocyanuric acid, 1, 3, 5-Triazine-2, 4, 6-triol and dichlorisocyanuric
acid, dichloroisocyanurate)
C3H3N3O3 + 2 Cl2, C3HCl2N3O3
+ 2HCl
cyanuric acid + chlorine, dichlorcyanuric acid + hydrochloric acid
C3H3N3O3 + 2OCl-, C3HCl2N3O3
+ 2HO-
cyanuric acid + hypochlorite ion, dichlorcyanuric acid + hydroxide ion
Stabilizer: also called cyanuric acid or conditioner.
A granular chemical added to the swimming pool water that provides a shield
to chlorine for protection from UV radiation.
Too much can result in chlorine lock.
Cyanuric acid can stabilize chlorine in swimming pools by protecting chlorine
in the water against the effects of the UV rays from the
sun.
Cyanuric acid is made by heating urea or some of its derivatives.
It is a selective herbicide, very toxic to barley and radishes.
It reacts with chlorine to give dichloro(iso)cyanuric acid in a chemical
equilibrium.
Stabilize swimming pool chlorine by using cyanuric acid at a minimum concentration
of 30 parts per million, ppm.
(1 ppm = 1 mg per litre.)
In the stabilization process, a portion of the chlorine residual is temporarily
bonded to the cyanuric acid molecule and protected from
the destructive effects of sunlight.
The nature of this bond is such that the chlorine demand is imposed upon
the system and continues to be released as long as a
demand exists.
As OCl- or HOCl is used up in the swimming pool more OCl-
is released from the dichloro(iso)cyanuric acid to re-establish the
equilibrium to maintain a constant amount of chlorine in the swimming
pool.
Other industrial chemicals are trichlorocyanuric acid and sodium dichlorocyanuric
acid.
The amount of cyanuric acid is kept constant in the swimming pool between
30 and 80 mg / L by the initial addition of any of the three
compounds then only hypochlorite should be added to keep the level of
free chlorine at 2 mg / L.
The equilibrium in the reaction stabilizes the concentration of OCl-.
If excess cyanuric acid is used, the chlorocyanuric acids do not absorb
the ultraviolet light from the sun.
To find the level of cyanuric acid in the swimming pool a reaction with
melamine forms a salt that precipitates and scatters light.
The turbidity is proportional to the amount of cyanuric acid.
The turbidity is measured by the depth of solution required in a standard
Nessler tube to just obliterate an object at the bottom of the
tube.
Anionic surfactants are measured by a similar salt formation chlorine
using methylene blue.
The salts formed are sufficiently lyophilic to transfer into organic solvents
and to be estimated by the depth of colour in the organic
solvent.
C3H3N3O3 + C3H6N6
--> (C3H3N3O3.C3H6N6)
cyanuric acid + melamine --> melamine cyanurate (melamine cyanuric
acid precipitate)
The test can be done with a small test-tube and a calibrated stick with
a black spot on the end.
The divisions on the stick where depth of spot seen is calibrated with
cyanuric acid concentration in ppm, follow Beer's law,
Concentration = Ke-a Depth.
During a swimming pool season, the conditioner may decrease from leakage,
swimmer activity causing splash out or drag out, and
maintenance operations, e.g. vacuuming and filter back washing.
Because of the slightly acidic pH of conditioner, addition of a small
quantity of PH plus or acid may be necessary to maintain pH at the
desired level.
If the conditioner concentration is too high, it can be lowered by dilution
with fresh top up water.
The CYA stabilizer reduces the free chlorine, which is what does the sanitizing,
and hence more must be added to maintain free chlorine
and an ORP within the range 650 mV to 750 mV.
Swimming pools not exposed to the sun, e.g. indoor swimming pools should
not be treated with CYA.
Some Australian State governments have banned the use of CYA in swimming pools.18.7.15 Algicides, control
of algae in swimming pools9.9.18 Effect of copper on the growth
of algae
If a swimming pool has an algae problem first vacuum and backwash, then
breakpoint chlorinate.
Use an algicide as a last resort.
Algae is the most common fouler of swimming pools because it is propagated
by air-borne spores.
When conditions favour their growth, e.g. heavy rain, intense sunlight,
and presence of nitrogenous materials, they can cause black and
green spots on swimming pool walls and form an algae bloom in the water
resulting in a sharp rise in pH, as the algae consume carbon
dioxide in the swimming pool water.
If algae bloom is present, use superchlorination followed by an algicide
to control it and prevent its reoccurrence.
Algicides should be used as a backup to a routine sanitation program.
Maintain a free chlorine residual in the swimming pool by sanitizing with
stabilized swimming pool chlorinating concentrates and adding
algicide according to the directions on the label.
Algae do not cause disease, but may provide an ideal substrate for bacteria.
Algicides as liquids or granules include copper and silver compounds,
Quat compounds, chlorine enhancer and herbicides.
They may be obtained formulated for a specific type of algae, e.g. green
algae, mustard algae, blue-green algae, black algae (black spot)
the hardest to treat, and be a bactericide.
Pink algae or red algae-like organisms may be a bacteria.
Chelated copper algicides that contain an ingredient to prevent the copper
from staining the swimming pool surfaces or producing
coloured water but do not affect the ability of copper to kill algae.
Copper may also be used in the equipment and plumbing in swimming pools.
Copper (II) sulfate was one of the original copper algicides as with aluminium
sulfate it also provides a flocculent.
However, it may harm some aquatic creatures in natural swimming pools
and stain solids in swimming pools.
Small concentrations of copper or silver ions produced by electrolysis
can be effective.
Materials similar to cationic surfactants are also used as algicides.
In addition to getting rid of algae, algicides extend the effectiveness
of chlorine residual.
While chlorine is an algicide, add additional quantities as a backup,
a maintenance dose.18.7.15.1 Green hair and
faded hair from swimming pools
Low calcium ion level, with low pH and high levels of copper and chlorine
from cheaper copper-based algicide, overuse of this algicide
or corrosive water may cause green hair, blue fingernails, green, brown
or blue water, stained swimming pool surfaces, and leaching of
copper from copper pipes, copper heating elements and bronze pump impellers.
It is not the chlorine that bleaches hair.
Oxidized metals in the water bind to the protein in the hair shaft and
deposit their colour.
The copper in algicide turns blond hair green.
Bleach added to a swimming pool may oxidize the copper, but the bleach
itself is not the cause of the colour.
The green precipitate is a mixture of copper sulfate and copper hydroxide
and is most noticeable in blond hair and especially bleached
hair where the hair shaft may lack the natural oils that reduce water
absorption.
To remove the green tint in hair, 1. Use folk remedies, e.g. wash the
hair in aspirin, tomato juice, lemon juice, baking soda, Alka Seltzer,
high pH shampoo.
2. Rinse the hair immediately after leaving the swimming pool.
3. Use a shampoo that chelates the copper.
Before swimming, prevent copper from binding to the hair by sealing the
hair cuticle with a hair conditioner.
Swimming pool chemicals, especially chlorine and bromine, react with the
sebum and oils that protect your hair, leaving the hair's
cuticle exposed.
This allows other chemicals to react with your hair, such as copper compounds,
which can give your hair a greenish tint.
Hair also becomes more susceptible to damage from the ultraviolet rays
of sunlight that break the bonds in keratin the protein in the
hair to cause roughness and split ends.
Pigment molecules also succumb to swimming pool chemicals and the sun,
so even if your hair does not turn green, it can become
lighter or faded.
The best way to prevent swimmers hair is to keep the swimming pool water
from soaking into your hair with a swim cap.
Limit exposure to swimming pool water by taking only occasional dips,
not letting the hair get wet, and by showering after exiting the
swimming pool.
The best treatment is to use a shampoo, but even a quick rinse in fresh
water will help remove the swimming pool chemicals.
Follow up with a conditioner to seal the cuticle of the hair's cuticle
and replenish its protective coating.
Healthy hair is less susceptible to swimmers hair than hair that already
has damage.
Also, coloured, permed or heat-treated hair is at greater risk for dryness
and colour loss from swimming than untreated hair.
If you swim a lot, reduce hair processing and keep up your cut so that
chlorine will not get in through split ends.
A special shampoo made just for swimmers may contain ingredients that
will chelate copper and other metals so that they do not
discolour the hair.
The shampoo may leave a waxy coating on the hair to prevent it from soaking
up swimming pool water.
Another shampoo is a clarifying shampoo to prevent build-ups that can
weigh your hair down and dull its shine.
Another option is to use a regular shampoo and follow-up with a leave-in
conditioner that contains a UV filter that give protection from
both the sun and the swimming pool water.18.7.16 Total dissolved solids
(TDS) water hardness, scale
Total Dissolved Solids, TDS, are a measure of all the dissolved chemicals
in the water, whether they are natural components of source
water, residues of treatment chemicals, swimmers wastes, or wind and rain
borne atmospheric pollutants.
They stay in the water and may cause staining, scaling and reduced chlorine
efficiency, if allowed to accumulate beyond recommended
limits.
All swimming pool water contains total dissolved solids.
Stabilizing and using chloroisocyanurate produces the least amount of
TDS.
It is estimated that TDS should be maintained at less than 1500 ppm.
Cyanuric acid causes no ill effects in swimming pool water but that it
may, by accumulation, indicates the onset of problems because of
TDS in the swimming pool.
The only practical way to remove dissolved solids from a swimming pool
is to remove a portion of the water in which they are dissolved.
The recommended rate of water removal per week is 1 to 3%.
In a 10 000 gallon swimming pool, this represents 100 gallons per week.
Hardness, total hardness is a measure of the calcium and magnesium content
of the water.
All water contains some natural hardness.
The amount will vary regionally, and from source to source.
Calcium hardness refers to the calcium content of the water.
If the calcium hardness level is too low, the water may be corrosive and
attack the materials of construction.
So a certain amount of hardness is necessary in water to control its tendency
to dissolve.
Hardness treatment will increase low water hardness and prevent etching,
pitting and corrosion of surfaces and metallic components.
The soluble white salt calcium chloride is used to raise the calcium hardness
or total hardness level of swimming pool water.
If the calcium hardness level is too high, the water may have a tendency
to form scale visible as crusty grey deposits and cloudy water
or deposits in piping that will y not function properly if their diameters
are decreased by scale formation.
Scale on swimming pool surfaces is unsightly and unattractive.
Scale is formed from calcium carbonate crystals when the calcium hardness,
pH or total alkalinity levels are too high.18.7.17 Cost of chlorination
Assess the cost at, say, 1.5 KW for 6 hours for 4 months and 1.5 KW for
4 hours for 8 months at $0.12 per kWh.
Amortize the cost of the equipment over, say, 7 years.18.7.18 Stabilized and unstabilized
swimming pools
In swimming pool waters, the free chlorine, HOCl, may be consumed by
the following:
1. Destroying bacteria and algae introduced by swimmers and by wind and
rain borne contamination,
2. Reacting with reduced metals such as Fe2+ to produce the
oxidized Fe3+ and chlorine ions,
3. Action of the ultraviolet energy of sunlight that converts free available
chlorine to the inactive chloride ion,
4. Oxidizing nitrogenous compounds such as ammonia (NH3) and
urea introduced into the water as components of perspiration, urine
and other bodily excretions.
Maintenance of free available chlorine residual at 1 ppm to 3 ppm.
Pre-conditioning the swimming pool with 30 ppm of conditioner, and using
a sanitizer to maintain that minimum, automatically provides
protection for a swimming pool against the effects of sunlight.
Most overseas countries require swimming pool operators to
measure free chlorine and ORP.18.7.19 Bromine products,
HBrO
Bromine is a halogen family used as a sanitizer or disinfectant to destroy
bacteria and algae in swimming pools and spas.
It is resistant to heat and rapid pH fluctuations and is available as
a tablet or as sodium bromide "bromide", a granular salt.
BCDMH (bromochlorodimethylhydantoin) is a bromine sanitizer.
When BCDMH dissolves in water, it produces hypobromous acid, HBrO, the
active form of bromine in swimming pool water.
Bromamines are by-products formed when bromine reacts with nitrogenous
compounds including swimmer waste.
Unlike chloramines, which are strong smelling and have low sanitizing
properties, bromamines are active disinfectants and do not smell,
although high levels are harmful to health.
A brominator is a mechanical or electrical device for dispensing bromine
at a controlled rate from a floater filled with bromine sanitizer
tablets.
Sodium bromide is used to raise the bromine levels in a swimming pool
before using bromine tablets.18.7.20 Filters
The three main types of swimming pool filters used in swimming pools are
sand filters, cartridge filters and diatomaceous earth, DE
filters.
Filter aids include the clarifiers, flocculents and coagulants that are
the inorganic salts of aluminium (alum) or organic polyelectrolytes,
and diatomaceous earth, called filter powder.
Sand filters use hard sharp silica or quartz or the zeolite clinoptilolite.
Filter micron size is in a unit of length equal to 1 millionth of a metre.
Microns are used to describe the pore size of swimming pool filter media.
Sand filters have openings of 25 to 30 microns, cartridge filters have
openings of 8 to 16 microns, and DE (diatomaceous earth) filters
have openings of 1 to 5 microns.
Zeolite used in sand filters have openings of 3 to 6 microns.
Flocculents, e.g. alum, and coagulants cause minute particles to clump
together to be trapped by the filter or fall to the bottom as "floc".
Flocculent are also used to clarify muddy swimming pool water with the
charged aluminium ion from alum.
Aluminium ion is also used in sticks to coagulate blood from shaving cuts
and in antiperspirants to coagulate sweat from pores under
the arm.
Alum sinks everything to the bottom to be vacuumed to waste and a small
amount of alum can also be used as a sand filter additive.18.7.21.0 Test kit for
chlorine levels in swimming pools
A test kit is a manual or electrical device used to measure specific chemical
residuals, levels or demands in swimming pool water.
Kits usually contain reagents, vials, titrants and colour comparators
for the tests.
The most common tests are as follows: pH, free available chlorine, combined
chlorine, total alkalinity, calcium hardness, cyanuric acid
and metals.
Test strips are small plastic strips with pads attached that have been
impregnated with reagents to test swimming pool water.
The strips are dipped into the water and the resulting colours are compared
to a colour scale to find the values.
Balanced water is the result when all the chemical parameters are within
the tolerance limits.
The most important parameters of water balance are pH, total alkalinity,
calcium hardness and temperature, as measured using the
Langelier Saturation Index.18.7.21.1 Acid demand of
swimming pools
Acid demand is the amount of acid required to bring high pH or total alkalinity
down to their proper levels is determined by an acid
demand test.
The acid demand test is a reagent test usually used in conjunction with
a pH test to find the amount of acid needed to lower pH or
total alkalinity.
Acid demand is the amount of acid that needs to be added to swimming pool
water to lower the pH and total alkalinity to acceptable
levels.18.7.21.3 Methyl orange
test for chlorine in swimming pools
Free chlorine bleaches methyl orange solution quantitatively
Make a stock solution of methyl orange: Dissolve 0.05 g methyl orange
in 100 mL of water.
Make a standard solution: Add 0.2 g NaCl to 10 mL of stock solution then
dilute to 100 mL.
Swimming pools will have different amounts of dissolved salt depending
on their treatment history.
The addition of 0.2 g of NaCl is an attempt to ensure roughly the same
ionic strength of the test sample as this may affect the accuracy
of the measurement.
The reagent appears to be stable in the dark for years.
Make a test solution: Add 3 mL of 6 M hydrochloric acid to 24 mL of standard
methyl orange solution.
Step 1: Put 0.25 mL of test solution in a test-tube.
Add 10 mL of swimming pool water.
1.1 It decolourizes instantly so at least 1 mg / kg chlorine present.
1.2 It does not decolourize instantly so insufficient chlorine in the
swimming pool.
Add more chlorine to the swimming pool and repeat the test.
Step 2: Put 0.5 mL of test solution in a test-tube.
Add 10 mL of swimming pool water.
2.1 It decolourizes instantly so at least 1.5 mg / kg chlorine present.
2.2 It does not decolourize instantly.
The swimming pool contains between 1.0 and present.
1.5 mg / kg of chlorine.
This is the best concentration.
Step 3: Put 0.75 mL of test solution in a test-tube.
Add 10 mL of swimming pool water.
3.1 It decolourizes instantly so at least 1.75 mg / kg chlorine present.
3.2 It does not decolourize instantly.
The swimming pool contains between 1.5 and 1.75 mg / kg of chlorine.
This concentration is too high.18.7.21.5 OTO test for
swimming pools, ortho-tolidine, ortho-toluidine
(ortho-toluidine, o-Toluidine, 2-Aminotoluene, 2-Methylaniline, CH3C6H4NH2)
The OTO test kit is seen as unreliable and is no longer used extensively.
If you find a yellow colour in the comparator and a clear liquid reagent,
then it is clear that this swimming pool is being tested by the
orthotolidine, or OTO method.
The OTO method has some advantages that have made it popular and widely
used.
It also has some major deficiencies.
OTO reacts easily with hypochlorite but reacts more slowly with chloramines,
so does not reliably measure "free chlorine", the chlorine
in the form of OCl- and HOCl.
The fact that it cannot easily distinguish free from combined chlorine
makes it a very doubtful aid to swimming pool operation.
Even worse, it creates a false sense of security, leading to erroneous
diagnosis of swimming pool problems, which delays remedial
action.
The swimming pool owner could test once, twice, or three times daily and
still have no idea whether enough free available chlorine was
present to protect the quality of the water.
A 1 ppm residual measured by OTO will provide far less protection to swimming
pool than a 1 ppm residual measured by the DPD
method.
Ortho-toluidine may be carcinogenic.18.7.21.6 DPD test for
swimming pools
DPD (C2H5)2NC6H4NH2
Diethyl-paraphenylene diamine.
DPD is an indicator reagent used to measure free available chlorine (DPD1)
and total chlorine (DPD3) bromine, ozone and other
oxidizers in water.
DPD is far superior to OTO.
The efficacy of chlorine is affected by many factors, including the sun,
temperature, water balance and the chlorine demand of the water.
DPD, is the phenylenediamine used to determine chlorine in water.
DPD free chlorine reagent powder pillows, DPD No. 1 tablets, DPD No. 3
tablets
DPD total chlorine reagent powder pillows.1. In the DPD calorimetric method to measure total
free chlorine, the intensity of the colour is directly proportional to the
amount of
chlorine present in the sample.
When DPD is added, the chlorine oxidizes it to magenta-coloured "Wurster
Dye", and colourless imine compound.
However, the test does not differentiate between the two forms of free
chlorine: HOCl, and OCl- and at high pH gives an inaccurate
reading.
DPD is a 2+ cation (NH3+ and N+H),
e.g. AQUANAL, often as a sodium salt.2. Measure chlorine levels in the range 0 -2 ppm
by simple colour comparison
colourless DPD amine cation + Cl2 --> magenta colour Wurster
dye free radical cation + colourless imine cation.3. Measure "combined chlorine" as monochloramine,
NH2Cl and dichloramine, NHCl2,
3.1 To measure monochloramine, add 0.1 mg KI to a 10 mL test sample acidified
to pH 6.2 to 6.5
NH2Cl + 3I- + H2O + H+ -->
NH4OH + Cl- + I3-
Then the I3- (and free chlorine in the sample) forms
the magenta Wurster dye
3.2 To measure the dichloramine, add >0.1 g of KI to the 10 L sample
NHCl2 + 3I- + H2O + 2H+ -->
NH4OH + 2Cl- + I3-
This last reaction gives total chlorine in the sample so the dichloamine
is measured by subtraction.4. When DPD, is added to the sample, chlorine oxidizes
the DPD to form two possible oxidation
product, magenta coloured compound called Wurster Dye, and a colourless
imine compound.
When small amounts of chlorine react, Wurster Dye is the favoured product.
When high levels of chlorine react the colourless imine compound is favoured,
leading to the apparent fading of the solution.
This method does not differentiate between the two forms of free chlorine:
HOCl, and OCl-.
The amounts of HOCl and OCl- present in solution are pH dependent.
If the process pH is allowed to rise too high, all free chlorine in solution
will be present as OCl-, the less efficient sanitizer, yet the
total free chlorine levels, as reported accurately by the DPD test, will
remain the same.5. The DPD test kit is in very common use.
DPD will distinguish free from combined chlorine.
A DPD residual will be fee available chlorine, not some combination of
HOCL, monochloramine, dichloramine and trichloramine.
It will effectively protect the swimming pool from contamination.
The method is simple and rapid.
A DPD NO. 1 tablet is dissolved in a measured amount of swimming pool
water to produce a coloured solution.
This colour is compared with the colour standards in the comparator to
find the amount of FAC that is present.
The amount of chloramine that is present can easily be determining by
adding a DPD NO. 3 tablet to the same test sample and
determining whether any additional colour develops.
The difference between this total chlorine measurement and the FAC test
result equals the chloramine content of the water.
Example: DPD No. 3 minus DPD No. 1 Chloramines 1.5 ppm to 1.3 ppm 0.2
ppm chloramines.6. Total Free Chloramine residual
This test method indicates precisely when remedial action is necessary
to prevent the accumulation of chloramines in swimming pool
water.
Bleaching out occurs when at above 10 ppm free available chlorine in a
swimming pool, a DPD test kit often indicates zero chlorine
because the reagent is being destroyed.
If you observe an initial pink colour that then rapidly fades, you probably
have far too much residual chlorine in the water.18.7.22 Starting to use a
filled swimming pool
1. Adjust the water level.
2. Check pump, filter, dosing equipment and gauges, and replace or repair
if faulty.
3. Check for algae infestation on walls and floor.
4. Superchlorinate until free chlorine residual of 10 milligrams per litre
is obtained.
This may be achieved by the addition of calcium hypochlorite or by running
the sodium hypochlorite dosing pumps while the
recirculation system is running.
5. Start up the pump and filter system.
6. Run for at least 48 hours before allowing swimmers into the swimming
pool.
7. Test swimming pool and make adjustment to pH water balance if required.18.7.23 Chloramines in swimming
pools
Chloramine (NH2Cl), dichloramine (NHCl2), trichloramine,
(NCl3)Organic chloramines, RNHCl, are quite stable and useful sources
of chlorine for bleaching, disinfection and oxidation when necessary
to kill bacteria.
However, chloramines can be eliminated from swimming pool water only by
using activated carbon filters.
In pure form it is an oily liquid that is highly reactive and explosive.
Some chemists who first discovered it or first used it were badly injured.
It may be formed in swimming pools when disinfecting.
If the pH of swimming pools is < 6.8, urea forms chloramines.
Chloramines are mildly toxic to bacteria but react with urea from swimmers'
urine to irritate the eyes and mucous membranes.
Nitrogen trichloride, not chlorine gas, causes the "swimming pool smell".
Nitrogen trichloride gas is very volatile and will escape from solution
in to the air to give a characteristic noxious chlorine smell.
It is toxic, it is also very corrosive and is responsible for stress corrosion
cracking of the fabric of buildings and ventilation systems.
chloramines may cause asthma in competitive swimmers and swimming pool
instructors.
The reactions of chlorine with ammonia and ammonia compounds formed from
organic waste to form chloramines are often written
as follows:
(1.) 4NH3 + 3Cl2 --> NCl3 + 3NH4Cl
ammonia + chlorine --> nitrogen trichloride (trichloramine) + ammonium
chloride
In hot water ammonia forms
(2.) NCl3 + H2O --> NH3 + 3HOCl
nitrogen trichloride (trichloramine) + hot water --> ammonia + hypochlorous
acid [chloric (I) acid]
There is no chemical that changes colour when someone urinates in a swimming
pool.
There are dyes that could cloud, change colour, or produce a colour in
response to urine, but these chemicals would also be activated
by other compounds, producing embarrassing false positives.
Also, ammonia and ammonia compounds react with HOCl to form chloramines.
(3.) Formation of monochloramine
NH3 + HOCl --> NH2Cl + H2O
ammonia + hypochlorous acid <--> chloramine + water
(4) Formation of dichloramine:
NH2Cl + HOCl --> NHCl2 + H2O
chloramine + hypochlorous acid <--> dichloramine + water
Chloramine may react with each other,
(5) Reactions of monochloramine with dichloramine
NH2Cl + NH2Cl --> N2 (g) + 3HCl
dichloramine + dichloramine, nitrogen + hydrochloric acid
or, in the presence of excess HOCl, produce nitrogen trichloride
Total equation: 2NH3 + 3HOCl --> N2 (g) + 3HCI
+ 3H2O
(6) Further addition of chlorine forms nitrogen trichloride, the "smell
of chlorine", that leaves "agitated" water and may cause eye irritation:
NH2Cl + HOCl --> NCl3 + H2O
dichloramine + hypochlorous acid, nitrogen trichloride + water.Ammonia (NH3) quickly combines with
chlorine to form bad smelling chloramines.
The chloramines are undesirable smelly compounds formed when insufficient
levels of free available chlorine react with ammonia and
other nitrogen containing compounds (swimmer waste, sweat, urine).
Chloramines are a threat to human health and are very poor sanitizers.
Chloramines can be destroyed by superchlorination.
Since all chlorinated sanitizers react with water to produce HOCl, chlorine
consumption depends on the amount of contamination that
is present.
Enough sanitizer must be added to meet the chlorine demand of the water
before a measurable residual can be maintained.
This amount depends on the amount of contamination present in make up
water, plus whatever is added by swimmer loading, rain,
dust and other external sources, e.g. nitrogenous wastes from swimmers'
bodies.
Whether they are as simple as ammonia in urine, or as complex as the components
in perspiration or saliva, they present special
problems when they accumulate in swimming pool water.
These contaminants react with HOCl to form compounds called chloramines,
or combined chlorine.
The combined chlorine reaction begins with one unit of ammonia, combining
with one unit of HOCl to form monochloramine (NH2Cl).
This reacts with another unit of HOCl to form dichloramine and finally
with a third unit of HOCl to produce trichloramine (NCl3).
It takes a fourth unit of HOCl to finally convert the original molecule
of ammonia into harmless nitrogen gas (N2) water and chloride
ion (Cl-) and a fifth unit of HOCl before a free available
chlorine residual can be measured.
These chloramines cause trouble in swimming pool water because they are
stable and persistent.
The monodichloramine and trichloramine from this first unit of ammonia
will survive and accumulate with the chloramines formed from
subsequent units of ammonia.
This is actually chlorine consumption, because HOCl combined with ammonia
forms chloramines.
Chloramines have very poor sanitizing power, so algae and bacteria can
grow.
In fact, they have such poor swimming pool sanitizing power that they
would be rated at only 0 to 10 on a relative activity scale with
HOCl rated at 10 000.
Chloramines could provide germ fee water if they were present at a concentration
of at least 25 to 50 ppm.
However, this concentration would create additional problems in a swimming
pool, because chloramines are very pungent and irritating,
causing eye irritation and chlorine odours at very low concentrations.
Unfortunately, the chlorine odours generated by chloramines lead many
people to think that too much chlorine has been added.
So, they stop adding chemicals and problems grow worse.
These symptoms are a signal to test and adjust pH, and add enough chlorine
to oxidize all the chloramines, establishing a free available
chlorine residual.
It is often very difficult to convince a swimming pool owner that insufficient
chlorination is the cause of chlorine odours, eye burn and
algae because the owner probably tested the swimming pool when a problem
was noticed, and got a very positive chlorine test
according to the test kit.
This is the most confusing problem caused by combined chlorine.
Some test methods measure it as part of a total chlorine residual.Recent studies have focussed attention on combined
chlorine in swimming pools, a common name for mono-, di- and trichloramine.
Chloramines and trihalomethanes, with chloroform, as the best known compound
in this group, are generally characterized as
disinfection by-products, because they emerge as secondary pollutants
out of the reaction between chlorine disinfectants and organic
pollutants in water.
Chloramines are formed in water by reaction between nitrogen hydrocarbons,
more especially ammonia
compounds like urea (NH2)2CO and chlorine following
reactions (1) (5)
1. NH4+ + H2O, H3O+
+ NH3 (decomposition of urea from urine, sweat)
2. NH3 + Cl2 --> NH2Cl monochloramine
3. NH2Cl + Cl2 --> NHCl2 dichloramine
4. NHCl2 + Cl2 --> NCl3 trichloramine
5. NH2R + Cl2 --> NHRCl alkylmonochloramine
Trichloramine (NCl3), formed in swimming pool water at pH <
6, is very volatile and responsible for a pungent, acid smell, which is
generally confused with a strong chlorine odour and, which is the main
cause for eye irritation in covered swimming pools.
Chloramines can be prevented forming by using CO2 as a pH corrector
to limit the low pH needed for trichloramine formation,
or by using alternative disinfection products, bromine, ozone or chlorine
dioxide (in pure form or as a complex compound,
e.g. Hydroxan, all with a low chloramine forming potential.
Once formed, chloramines can be reduced with:
1. active charcoal in granular form in filters, in powder or as hydroanthracite
in double layer filters)
2. breakpoint chlorination, with chlorine at least ten times above the
chloramine concentration in swimming pool water.
As chloramines can hardly be found in open air swimming pools because
of the almost immediate destruction by incident sunlight, the
idea grew years ago to use artificial sunlight as a chloramine reduction
tool.
The chloramine separator of P. Kaas used ultraviolet and infrared light
and was used with changing success from the years 1975-80 on.
The use of UV light was promoted as best available technique in water
treatment of swimming pools by the Flemish Technology
Research Institute VITO.
Recently, new UV systems became available on the market using low or medium
pressure UV lamps.
Low pressure lamps contain mercury vapour at about 10-3 bar
and emit monochromatic light of 254 nm while the medium pressure
One type operates at mercury vapour pressures that emits polychromatic
light, including the 254 nm wavelength.
This is near the optimum wavelength of 245 nm at which monochloramine,
the precursor of dichloramine and trichloramine, breaks.
down by photochemical oxidation.
Thus low pressure lamps focus on the breakdown of monochloramine, while
medium pressure lamps attack dichloramine and
trichloramine.18.7.24 Total chlorine
Total chlorine is the sum of combined chlorine and free chlorine, i.e.
the total amount of chlorine in the swimming pool water.
When chlorine is added to water in a newly filled swimming pool, some
of it is consumed in the process of destroying algae, bacteria
and other oxidizable material in the water.
The amount of chlorine consumed in this process is referred to as the
chlorine demand of the water.
Once the chlorine demand is satisfied, any additional chlorine added is
referred to as chlorine residual.
With a DPD test kit, DPD1 shows free available chlorine and DPD3 shows
total chlorine.
The difference, if any, is the level of combined chlorine.18.7.25 Combined chlorine
Combined chlorine is the measure of chlorine that has attached itself
to other molecules or organisms, usually ammonia or nitrogen
compounds.
Most of these compounds are present as unwanted chloramines.
So combined chlorine is the chlorine that has combined with ammonium.
compounds or organic matter containing nitrogen to form chloramines.
Combined chlorine residual is the chlorine combined with simple nitrogen
compounds such as ammonia and urea as chloramine that is
non-effective as a sanitizer compared to free available chlorine.
Bactericidal properties of combined chlorine (i.e. chloramines) is only
about one hundredth that of a similar level of free chlorine in
water.
With a DPD test kit, DPD1 shows free available chlorine and DPD3 shows
total chlorine.
The difference, if any, is the level of combined chlorine.18.7.26 Chlorinator
A chlorinator is a mechanical or electrical device for adding chlorine
to a swimming pool at a controlled rate.
It is usually a floater filled with tablets of chlorine or an in-line
feeder.18.7.27 Stabilized chlorine
Stabilized chlorine is a family of organic chlorine compounds that contain
stabilizer (cyanuric acid or iso-cyanuric acid) to protect the
chlorine from the degrading UV rays in sunlight.
Most common types are dichlor and trichlor.
The granular form is dichlor and the tablet or stick form is trichlor.
Stabilized chlorine should be used with care, to avoid problems such as
chlorine lock that may be caused by overstabilization.18.7.28 Chlorine demand
Chlorine demand is the amount of chlorine necessary to oxidize all organic
matter (bacteria, algae, chloramines, ammonia and nitrogen
compounds) in the swimming pool water.18.7.29 Chlorine enhancer
A chlorine enhancer is a chemical compound used in conjunction with chlorine,
which makes the chlorine do better as an algicide.18.7.30 Chlorine generator:
A chlorine generator is an electrical device that generates chlorine from
a salt solution.
The salt solution may be in a separate tank or may be in the swimming
pool itself.18.7.31 Chlorine lock:
Chlorine lock occurs if the level of cyanuric acid (stabilizer) in the
swimming pool water is much over 80 ppm, the chlorine becomes
trapped and is unable to oxidize effectively.
Despite being able to measure normal chlorine levels, the Redox potential
is very low, indicating a lack of oxidizer.
The only way to fix this is to drain some of the swimming pool water and
refill the swimming pool.
Care should be taken when using stabilized chlorine products (dichlor
or trichlor) to avoid the level of cyanuric acid increasing too much.18.7.32 Chlorine neutralizer
A chlorine neutralizer is a chemical used to deactivate or destroy chlorine.
It is used in better test kits to prevent the bleaching effect of the
chlorine and so to increase the accuracy of the tests.18.7.33 Disinfectants
Disinfectants are chemicals, elements or processes that destroy vegetative
forms of micro-organisms and other contaminants.
Examples are chlorine, bromine, ionizers, ozonators and copper and silver
algicides.
Only chlorine and bromine are used as oxidizers, disinfectants and sanitizers
in swimming pools.
Hydrogen peroxide is an unstable, colourless liquid, which is used as an
antiseptic in the home.
It can be used as an oxidizing agent in swimming pools.
It is NOT compatible with the swimming pool wizard.18.7.34 Ionizers for swimming
pools
A swimming pool water sanitizer that uses electricity to generate metal
ions, usually copper and silver.
It works by passing a current through a set of electrodes.
The copper is an algicide and algaestat, while the silver is a bactericide.
Ionizers can significantly reduce chlorine consumption.
If the ion levels get too high, problems with staining or discolouration
of the swimming pool water occur.18.7.35 Nitrogen pollution
Nitrogen pollution causes algae to bloom and disables chlorine in swimming
pools.
It is introduced into the swimming pool water by rain and by swimmers.
Maintaining proper chlorine levels will prevent nitrogen from becoming
a problem.
Superchlorination can destroy nitrogen and nitrogenous compounds.18.7.36 Organic waste
Organic waste (swimmer waste, bather waste), refers to the soap, deodorant,
suntan lotion, body oils, sweat, spit, urine.
introduced into the swimming pool water by swimmers, as well as the leaves,
dust and insects that end up in the swimming pool.
The organic waste may form undesirable chloramines, which require large
amounts of chlorine or non-chlorine shock to be destroyed.
There is a famous myth that a special substance may be added to swimming
pool water to reveal the presence of urine and embarrass
the urinating swimmer.
No such substance exists.
Such a substance would probably react to other body excretions, e.g. sweat,
and use of it would tempt naughty children to discolour
the the water near another swimmer than swim away.18.7.37 Redox potential
Redox potential (Reduction-Oxidation Potential) is a measurement of the
ability of the chlorine oxidizer to oxidize contaminants versus
the ability of the contaminant, e.g. algae, to reduce the oxidizer.
It is an indication of the level of free available oxidizer in the swimming
pool water.
ORP is generally used with automated dosage systems and can give a fair
idea of the sanitation of the swimming pool water.
It is not a measure of the total or available chlorine.
Sometimes called ORP.18.7.38 Biguanides sanitizers
Biguanides is the name for a certain class of sanitizers using the polymer
PHMB, the only non-halogen sanitizer available for
swimming pool use.
Soft Swim and Baquacil are manufacturers of this sanitizer.
Biguanides are NOT compatible with the swimming pool Wizard.18.7.39 Contaminants in swimming
pools
Contaminants is the general name for any micro particle or organism that
reduces swimming pool water clarity, quality or presents
health hazards.
Filtering, oxidizing and sanitizing are necessary to destroy the contaminants.18.7.40 Corrosion in swimming
pools
The effects of an acidic swimming pool environment when the pH and / or
alkalinity are very low.
Corrosion in the form of etching, pitting or erosion of swimming pool
equipment and surfaces is the result.
Corrosion may also be caused by misuse of acid or by soft water.18.7.41 Defoamers
Foam is a froth of bubbles on the surface of the swimming pool water.
It usually comes from overuse of algicides, but may also be caused by
soaps, oils or other contaminants carried by swimmers.
Enzymes may be used for foam control.
A defoamer (anti-foam) is a chemical added to swimming pool water to
destroy the foam.
These products do not remove the source of the foaming.
Shocking and superchlorination may help prevent foaming.
Controlled use of certain of the cheaper algicides can prevent their resulting
in foaming.18.7.42 Stains in swimming
pools
A stain is a discolouration or a coloured deposit on the walls or bottom
of a swimming pool.
Stains are usually the result of metals such as iron, copper or manganese
in the swimming pool water.
The stains may be green, grey, brown or black.
They may discolour the swimming pool water without affecting the clarity.
Sometimes a sequestering agent, chelating agent or stain remover
may remove them.
If that does not work, the easiest way to remove the stains is to drain
and acid wash the swimming pool.
Stain inhibitor: also called a sequestering or chelating agent.
A chemical that will combine with dissolved metals in the swimming pool
water to prevent the metals from coming out of solution and
so avoiding discolouration of the water or stains.
Iron is a natural element that can cause the swimming pool water to become
clear brown or green in colour.
It can also result in staining of the swimming pool surfaces.
Iron can be controlled by the addition of a suitable sequestering or chelating
agent.18.7.43 Langelier saturation
index
Langelier saturation index (LSI, Langelier index, saturation index),
is used to find swimming pool water balance according to the
levels of pH (total alkalinity) and calcium.
It measures the relative concentration of Ca2+ and CO32-
to indicate if CaCO3 will precipitate out of solution and affect
the clarity of
the pool water or form an unsightly scale that may damage pumps.18.7.44 Liquid acid for swimming
pools
Liquid acid (hydrochloric acid, muriatic acid), is used for lowering
pH, total alkalinity and for acid washing in swimming pools.18.7.45 Lithium hypochlorite,
LiClO
Lithium hypochlorite, LiClO, is a dry granular chlorine compound with
35% available chlorine and has a pH of 10.7.
It dissolves quickly and completely.
It can be used to superchlorinate vinyl liner swimming pools, painted
swimming pools, fibre glass swimming pools and "hot tubs".18.7.46 Magnesium hardness
Magnesium hardness is a measure of the amount of magnesium dissolved in
swimming pool water.
It is part of total hardness.18.7.47 Make-up water, fill
water
Make-up water (fill water, top up water, refill water), is the water
used in filling or topping up the swimming pool.
It is the water used to replace swimming pool water lost to evaporation,
splash out, leaks and back-washing in swimming pools.18.7.48 Marbelite
Marbelite ("plaster"), is a mixture of white cement and white marble
dust used as an interior finish of a swimming pool.
It can be given a colour or it may be left white.18.7.49 Non-chlorine shock,
potassium peroxymonosulfate
Non-chlorine shock is a granular form of potassium peroxymonosulfate (potassium
monopersulfate, MPS, "Oxone"), commonly used
triple salt oxidizing agent, 2KHSO5KHSO4K2SO4,
used to oxidize materials such as micro-organisms, contaminants (ammonia,
nitrogen, swimmer waste) or chloramines in swimming pools.18.7.50 ORP
ORP (Oxidation-Reduction Potential, Redox Potential) is a measure of
the ability of the oxidizer, e.g. chlorine, to oxidize contaminants
versus the ability of the contaminants, e.g. algae, to reduce the oxidizer.
It is an indication of the level of free available ability of the oxidizer
in the swimming pool water.
ORP is generally used with automated dosage systems and can give a fair
idea of the sanitation of the swimming pool water.
It is not a measure of the total or available chlorine.18.7.51 Oxidizers
An oxidizer is any compound that removes or destroys organic waste and
organic compounds in the swimming pool water.18.7.52 OzonatorOzone
An ozonator is an electrical device that produces ozone that is introduced
into the swimming pool water as a sanitizer.18.7.53 Phenol red Phenol red: C19H14O5S (acid-base
indicator), A chemical reagent dye used to test pH.
It can measure pH from 6.8 to 8.4.
The tablet form usually incorporates a chlorine neutralizer for more accurate
results. ppm: The abbreviation for parts
per million.
It is a method of assigning value to concentrations of chemicals in the
swimming pool water.
Many of the common swimming pool water tests, as well as acceptable ranges,
are stated as ppm.
One ppm is equivalent to 1 milligram of something per litre of water (1
mg / litre).18.7.54 Precipitation
Precipitation is material forced out of solution will settle, stain,
scale or remain suspended in the swimming pool water.18.7.55 Pump strainer basket:
A pump strainer basket is a device placed on the suction side of the pump,
which contains a removable strainer basket designed to trap
large debris in the swimming pool water flow without causing restriction.
It is sometimes called a Pump Leaf Trap.
swimming pool pumps can cause severe injury to small children if they
are small enough to sit over the pump.
Some children in Australia have had their lower colon and anus pulled
out by a swimming pool pump.18.7.56 QAC (quaternary ammonium
compounds:)
QAC, Quaternary ammonium compounds (Quats, QAC) are a type of algicide
composed of ammonia compounds.
They are also effective algaestats for certain types of algae in swimming
pools.Residual bromine
The amount of free available bromine remaining in the swimming pool water
after the bromine demand has been satisfied.Residual chlorine
The amount of free available chlorine remaining in the swimming pool water
after the chlorine demand has been satisfied.Sanitize
To kill all micro-organisms, including bacteria and algae, and to remove
unwanted contaminants.Scale
The precipitate that forms on surfaces in contact with swimming pool water
when the calcium hardness, pH or total alkalinity
levels are too high.
Scale may appear as grey, white or dark streaks on the plaster, fibreglass
or vinyl.
It may also appear as a hard crust at the waterline.Scum
The foreign matter that floats to the surface of the swimming pool water
and forms a layer or a film.
It can also refer to a residue deposited on the tiles or walls of the
swimming pool.Sediment
The solid material that precipitates out of the swimming pool water and
settles to the floor of the swimming pool.18.7.57 Sequestering agent,
chelating agent
A chemical or compound that combines with dissolved metals or minerals
in the swimming pool water to prevent them from coming
out of solution, thus colouring the swimming pool water or causing stains.
A sequestrant is a chemical that holds metals in solution and helps prevent
scaling.18.7.58 Sodium bicarbonateSodium bicarbonate,
Sodium hydrogen carbonate, baking soda, "bicarb"
A base used to raise total alkalinity in swimming pool water with only
a slight effect on the pH.
Sodium bicarbonate can only raise the pH of the swimming pool water to
8.5, regardless of the amount used.
Do not add large quantities at one time.
A correspondent from New Zealand reports that he got great results, sparking
water, excellent control and minimal chemical use by
raising the total alkalinity to 200 ppm + using sodium bicarbonate and
in the process got a stable pH of 8.3, which he almost never
had to test for.
Also, the chemical was safe to use.
The correspondent compensated for the higher pH by running the swimming
pools with a FAC of around 4 ppm and not letting it drop
below 1 ppm.
He only used sodium hypochlorite diluted to 8% to give a good shelf life.
This procedure was satisfactory for about 20 swimming pools.
In this procedure the ORP is above 650 mV at pH 8.4 and 4 ppm free chlorine,
but less than 750 mV.
650 mV to 750 mV is the recommended range for effective sanitation.
Assuming he did not use stabilizer or did not need to, he probably needed
to top up the bicarbonate relatively frequently to keep it at
around 200.
A lower alkalinity and a weekly dose of acid, to give lower pH and higher
ORP could allow free chlorine to be reduced to about 1 ppm.
To maintain a stable pH level, add about 100 mg / kg of sodium bicarbonate
to water, i.e. about 6 kg in a 60, 000 litre pool.
Or
Add 1.5 pounds of baking soda for each 10, 000 gallons of water to raise
total alkalinity by 10 ppm, for total alkalinity within 80 to
150 ppm.
Maintain a proper level of total alkalinity to minimize changes in pH when
acidic or basic chemicals or contaminants enter the water,
reducing chloramine formation, corrosivity of water, eye irritation and
unpleasant odours, while improving bactericidal effectiveness.18.7.59 Sodium carbonateSodium carbonate:
Also called soda ash.
A base that is used to raise the pH of acidic (below pH 7.0) swimming
pool water.18.7.60 Sodium dichlor
Sodium dichlor is a granular, stabilized organic chlorine compound providing
56% or 62% available chlorine that has a pH of 6.9,
used for regular chlorination.
It should be used with caution for superchlorination because as it can
cause the stabilizer level to rise too high, resulting in chlorine lock.18.7.61 Sodium monopersulfate
Sodium monopersulfate is the active ingredient and chemical name of a non-chlorine
shock treatment or non-chlorine oxidizer of
swimming pool water.18.7.62 Sodium persulfate
Active ingredient and chemical name of a non-chlorine shock treatment
or non-chlorine oxidizer of swimming pool water.18.7.63 Sodium sulfite
Sodium sulfite: A chemical that can be used to neutralize chlorine
or dechlorinate swimming pool water.18.7.64 Sodium thiosulfate
Sodium thiosulfate: A chemical that can be used to neutralize chlorine
or dechlorinate swimming pool water.18.7.65 Suspended solids
Insoluble solid particles that either float on the surface or are in suspension
in the swimming pool water causing cloudiness.
They may be removed by filtration, but if the particles are too small,
a flocculent or coagulant is necessary to enable the filter to trap them.18.7.66 Total dissolved solidsTDS (Total Dissolved Solids),
is a measure of everything that has ever dissolved in the swimming pool water
and all the matter that is
in solution.
The only way to lower TDS is to drain part of the swimming pool water
and replace it.18.7.67 Trichlor
Trichlor is a slow dissolving, tablet or granular stabilized organic chlorine
compound that provides 90% available chlorine and has a pH
of 2.9.
It must be dispensed using a floating feeder or an in-line chlorinator.
Trichlor contains cyanuric acid that prevents the chlorine from being
destroyed by the ultraviolet rays of the sun.
When using trichlor, the cyanuric acid level needs to be checked regularly
to avoid chlorine lock.18.7.68 Turbidity
See: Turbidity, (Commercial)16.0 Tests for turbidity
Turbidity is the cloudy condition of the swimming pool water because of
the presence of extremely fine particles in suspension that are
able to pass through the filter.
Adding a flocculent or coagulant will clump the particles together so
they can be trapped in the filter.
Devices called turbidity meters can be used to measure turbidity.18.7.69 ZeoliteZeolite: An alternative to quartz or
silica for use in sand filters for swimming pools.
It is typically clinoptilolite, the specific zeolite suitable for swimming
pool water conditions.
Zeolite can provide filtration down to 3 microns, is able to absorb heavy
metals such as iron or manganese, and absorbs ammonia and
nitrogen compounds.
Zeolite can also absorb chloramines and is regenerated by washing in salt.
Being less dense than quartz, 60% to 70% of the weight of quartz is used.
Zeolite is also claimed to reduce back washing by 50%.18.7.70 Water hardness
Soft water
Soft water has a low calcium content that can cause etching of swimming
pool surfaces, so water hardness should be increased with
calcium chloride.
Hard water
Swimming pool water that is high in calcium, magnesium or other salts,
which makes it difficult for soap to lather.
Hard water also has a tendency to form scale.
Calcium hardness: The amount of calcium dissolved in the swimming pool
water.
It is usually measured as calcium carbonate.
Total hardness:
The amount of calcium, magnesium and other salts dissolved in the swimming
pool water.
Hardness and water temperature.
When all the parameters are in balance, the swimming pool water will neither
be corrosive nor scaling.